The present invention relates to a recording medium represented by an optical disk using inorganic nanoparticles and nanoparticles of a metal chalcogen compound. More particularly, the invention relates to a recording medium used in an optical recording using near field light in order to increase recording density, and to a method for recording the same. The term xe2x80x9cnanoparticlesxe2x80x9d as used herein means ultrafine particles having an average particle size ranging from 1 nm to 50 nm.
Densification and sensitization of optical recording materials have extensively been improved. Laser beams having a wavelength of 600 nm or more have hitherto been used, and recording media have also been developed and designed so as to exhibit the optimum performance within this wavelength region. It is well known that a reduction in the wavelength of light to one nth results in an nxc3x97n-fold increase in the recording density of information. It has therefore been advanced to study high-density recordings using short-wave lasers having a wavelength of about 400 nm. However, when the use of a laser having a shorter wavelength is attempted for making a higher density recording, it becomes impossible to maintain optical transparency of the recording media themselves. Further, even when an increase in NA is intended, it becomes difficult to form a recording mark of 100 nm or less because of the diffraction limit of light.
In recent years, in order to achieve high-density recordings exceeding the diffraction limit of light, recording methods utilizing near field light have been proposed. However, as the near field light is away from its generation source, its optical intensity is exponentially decreased. It is therefore necessary to use various amplification functions in combination. For example, it has been known that the shape or material of a near field light probe is selected, or that it is coated with a metal to utilize the coupling with metal surface plasmon. On the other hand, as a method of giving the function to the recording medium side, a method of arranging on an upper portion of a recording layer a mask layer in which a minute opening can be formed by light, as described, for example, in Japanese Patent Laid-Open Nos. 250493/1999 and 242969/2000, and utilizing near field light generated therefrom. Further, it has been studied that the use of silver oxide in this mask layer locally develops metallic silver to generate local plasmon there, thereby amplifying optical intensity.
However, all of the above are directed to improvements from the viewpoint of the generating method of near field light or the amplification of optical intensity, and in other words, techniques for allowing them to reach the optical intensity of the recording media. However, these alone do not necessarily give sufficient intensity. That is to say, these do not have the viewpoint of increasing the sensitivity to light of the recording medium side.
On the other hand, as a technique using fine particles in a recording medium, Japanese Patent Laid-Open No. 62239/1993 discloses a technique using ultrafine semiconductor particles of Ge or Si formed by spattering and having a particle size distribution. This technique intends to make a wavelength multiple recording utilizing the difference in quantum size effect between the ultrafine particles different in size, in order to improve recording density without depending on shortening of the wavelength of a laser or an increase in NA, and is basically different from the invention in which the optical sensitivity of an energy-irradiated portion is improved using homogeneous nanoparticles.
An object of the invention is to efficiently form a recording mark with a reduced size, for making a high-density optical recording.
Another object of the invention is to provide a recording medium with which a high-density optical recording can be made.
A still other object of the invention is to provide a recording method realizing a high-density optical recording.
Other objects and effects of the invention will become apparent from the following description.
The above-described objects of the invention have been achieved by the following embodiments.
1) An optical recording method which comprises:
making a recording with near field light on an optical recording medium comprising a substrate having provided thereon a particle layer containing particles having an average particle size ranging from 1 to 50 nm;
2) The optical recording method according to the above embodiment 1), wherein the particle layer is a recording layer and the particles comprising particles of a metal chalcogen compound;
3) The optical recording method according to the above embodiments 1) or 2), wherein the particle layer of the optical recording medium is arranged 5 nm to 100 nm apart from a generation source of near field light, and a heat-resistant protective layer is provided on the particle layer as a layer closer to the generation source of near field light to give multiple layer constitution;
4) The optical recording method according to any one of the above embodiments 1) to 3), wherein the recording is carried out using a recording unit comprising a recording head having integrated therein a plurality of probes for generating near field light, and a part of the recording head is brought substantially in contact with the optical recording medium;
5) The optical recording method according to any one of the above embodiments 1) to 4), wherein the particles are monodisperse particles;
6) The optical recording method according to any one of the above embodiments 1) to 5), wherein the particle layer is formed by coating.